Conductivity and Pseudocapacitance Optimization of Bimetallic Antimony-Indium Sulfide Anodes for Sodium-Ion Batteries with Favorable Kinetics.

Metal sulfides show promise for use in alkali-ion batteries because of their high theoretical capacities. However, their poor cycling stability and rate performance hinder their further development. To avoid these issues, In ₂ S ₃ into Sb ₂ S ₃ is introduced to improve its electrochemical properties by optimizing its crystal structure and sodium storage mechanism. A heterostructure composed of In ₂ S ₃ and Sb ₂ S ₃ shows a unique morphology of formicary microspheres, which provide abundant channels for fast transfer of sodium ions, large surface area for a high pseudocapacitance effect, and enough voids to relieve volume expansion. A sodium-ion battery containing the bimetallic sulfide anode exhibits a high reversible capacity of 400 mA h g ^-1 and long cycle life of about 1000 cycles. Similarly, a high capacity of ≈610 mA h g ^-1 is achieved for a lithium-ion battery containing the anode. During sodiation/desodiation, the synergistic effect of In ₂ S ₃ and Sb ₂ S ₃ enhances electronic conductivity and supports the host structure, preventing collapse. The cycling performance and rate performance of the In ₂ S ₃ -Sb ₂ S ₃ anode are further improved by wrapping the electrode with carbon nanotubes. Even at a high current density of 3.2 A g ^-1 , this carbon composite structure still shows a capacity of about 355 mA h g ^-1 .